docs: def Wang_Chiang_Lu(m, x, rhol, rhog, mul, mug, D, roughness=0, L=1):
      r'''Calculates two-phase pressure drop with the Wang, Chiang, and Lu (1997)
      correlation given in [1]_ and reviewed in [2]_ and [3]_.
  
      .. math::
          \Delta P = \Delta P_{g} \phi_g^2
  
      .. math::
          \phi_g^2 = 1 + 9.397X^{0.62} + 0.564X^{2.45} \text{ for } G >= 200 kg/m^2/s
  
      .. math::
          \phi_g^2 = 1 + CX + X^2 \text{ for lower mass fluxes}
  
      .. math::
          C = 0.000004566X^{0.128}Re_{lo}^{0.938}\left(\frac{\rho_l}{\rho_g}
          \right)^{-2.15}\left(\frac{\mu_l}{\mu_g}\right)^{5.1}
  
      .. math::
          X^2 = \frac{\Delta P_l}{\Delta P_g}
  
      Parameters
      ----------
      m : float
          Mass flow rate of fluid, [kg/s]
      x : float
          Quality of fluid, [-]
      rhol : float
          Liquid density, [kg/m^3]
      rhog : float
          Gas density, [kg/m^3]
      mul : float
          Viscosity of liquid, [Pa*s]
      mug : float
          Viscosity of gas, [Pa*s]
      D : float
          Diameter of pipe, [m]
      roughness : float, optional
          Roughness of pipe for use in calculating friction factor, [m]
      L : float, optional
          Length of pipe, [m]
  
      Returns
      -------
      dP : float
          Pressure drop of the two-phase flow, [Pa]
  
      Notes
      -----
  
      Examples
      --------
      >>> Wang_Chiang_Lu(m=0.6, x=0.1, rhol=915., rhog=2.67, mul=180E-6,
      ... mug=14E-6, D=0.05, roughness=0, L=1)
      448.29981978639154
  
      References
      ----------
      .. [1] Wang, Chi-Chuan, Ching-Shan Chiang, and Ding-Chong Lu. "Visual
         Observation of Two-Phase Flow Pattern of R-22, R-134a, and R-407C in a
         6.5-Mm Smooth Tube." Experimental Thermal and Fluid Science 15, no. 4
         (November 1, 1997): 395-405. doi:10.1016/S0894-1777(97)00007-1.
      .. [2] Kim, Sung-Min, and Issam Mudawar. "Universal Approach to Predicting
         Two-Phase Frictional Pressure Drop for Adiabatic and Condensing Mini/
         Micro-Channel Flows." International Journal of Heat and Mass Transfer
         55, no. 11-12 (May 2012): 3246-61.
         doi:10.1016/j.ijheatmasstransfer.2012.02.047.
      .. [3] Xu, Yu, Xiande Fang, Xianghui Su, Zhanru Zhou, and Weiwei Chen.
         "Evaluation of Frictional Pressure Drop Correlations for Two-Phase Flow
         in Pipes." Nuclear Engineering and Design, SI : CFD4NRS-3, 253 (December
         2012): 86-97. doi:10.1016/j.nucengdes.2012.08.007.
      '''
      G_tp = m/(pi/4*D**2)
  
      # Actual Liquid flow
      v_l = m*(1-x)/rhol/(pi/4*D**2)
      Re_l = Reynolds(V=v_l, rho=rhol, mu=mul, D=D)
      fd_l = friction_factor(Re=Re_l, eD=roughness/D)
      dP_l = fd_l*L/D*(0.5*rhol*v_l**2)
  
      # Actual gas flow
      v_g = m*x/rhog/(pi/4*D**2)
      Re_g = Reynolds(V=v_g, rho=rhog, mu=mug, D=D)
      fd_g = friction_factor(Re=Re_g, eD=roughness/D)
      dP_g = fd_g*L/D*(0.5*rhog*v_g**2)
  
      X = (dP_l/dP_g)**0.5
  
      if G_tp >= 200:
          phi_g2 = 1 + 9.397*X**0.62 + 0.564*X**2.45
      else:
          # Liquid-only flow; Re_lo is oddly needed
          v_lo = m/rhol/(pi/4*D**2)
          Re_lo = Reynolds(V=v_lo, rho=rhol, mu=mul, D=D)
          C = 0.000004566*X**0.128*Re_lo**0.938*(rhol/rhog)**-2.15*(mul/mug)**5.1
          phi_g2 = 1 + C*X + X**2
      return dP_g*phi_g2